A number of thermoplastic polymers, elastomers, and their blends (thermoplastic/elastomer composite compositions) are very difficult to plasticize. In particular, thermoplastic/elastomer composite compositions that include one or more thermoplastic polymers and one or more elastomers, such as EPDM, are difficult to plasticize because it is difficult to find plasticizers that are sufficiently compatible with the composite compositions. Consequently, exuding (bleeding) of plasticizer to the surfaces of an article comprising the thermoplastic/elastomer composite composition frequently occurs upon cooling and crystallization of the composite composition.
Hydrocarbon-based processing oils such as naphthenic oils or paraffinic oils are usually used to plasticize thermoplastic/elastomer composite compositions containing elastomers such as EPDM. While hydrocarbon-based processing oils can be used to plasticize such composite compositions with partial success, the resulting plasticized compositions lack advantageous low temperature properties. Moreover, the processing oils have a tendency to exude (bleed) to the surfaces of articles manufactured from composite compositions. Attempts to use conventional linear dibasic acid esters, such as dioctyl adipate or di-2-ethylhexyl sebacate, or phthalate esters, such as di-2-ethylhexyl phthalate, have also been unsuccessful since such conventional ester plasticizers ate either incompatible with composite compositions, resulting in exudation of the plasticizer, or are too volatile for many thermoplastic/elastomer composite composition uses.
U.S. Pat. No. 5,290,886 teaches using organic ester plasticizers to plasticize thermoplastic elastomers comprising a blend of a thermoplastic polyolefin and an elastomer to lower the glass transition temperature (Tg) of both the elastomer and the polyolefin phases and to improve impact strength at low temperatures. The '886 patent neither discloses nor suggests using the cyclic dimerate and/or cyclic trimerate esters disclosed herein, and states that “polymeric dibasic esters and aromatic esters were found to be significantly less effective” (column 3, lines 62–64).
Surprisingly and unexpectedly, particular dimerate and/or trimerate esters designed to have very low polarity act as efficient plasticizers for thermoplastic/elastomer composite compositions. The resulting plasticized compositions have excellent low temperature properties and exhibit little or no tendency of the plasticizer to exude or bleed to a surface of the composite composition. Using the low polarity dimerate and/or trimerate esters as a plasticizer gives the thermoplastic/elastomer composite compositions an advantageous balance of flexibility, impact resistance, and strength.